Invoice Late Fee Calculator

Calculate the late fee owed on an overdue invoice instantly. Supports flat fee or percentage-based late fees, daily/monthly accrual, and compounding to protect your cash flow.

Mathematical Audit

Invoice Late Fee Formulas

Late fees can be calculated as a flat amount, a simple periodic percentage, or with compounding.

Simple Late Fee = Invoice Amount × (Monthly Rate / 30) × Days Overdue
Monthly Percentage Fee = Invoice Amount × Monthly Rate % × Months Overdue
Compound Late Fee = Invoice Amount × (1 + Daily Rate)^Days − Invoice Amount
Total Amount Due = Original Invoice + Accrued Late Fee

The most common commercial late fee in the US is 1.5% per month (18% APR). Some states cap late fee interest rates — always check local laws before charging late fees.

Operational Guide

How to Use the Invoice Late Fee Calculator

1

Enter the original invoice amount

Input the full invoice amount before any partial payments.

2

Enter the number of days overdue

Count from the invoice due date to today. Most net-30 invoices become overdue on day 31.

3

Choose flat fee or percentage rate

Select whether you charge a flat dollar amount or a percentage (e.g., 1.5%/month). Check your contract terms.

4

Select the accrual frequency

Late fees can accrue daily, monthly, or as a one-time charge. Monthly is most common for B2B invoices.

Real-World Scenario Example

"A freelancer sent a $5,000 invoice that is now 45 days overdue. Their contract specifies 1.5% per month."

Inputs

invoiceAmount:5000
daysOverdue:45
feeType:percentage
monthlyRate:1.5
accrualFrequency:monthly

Result

45 days = 1.5 months. Late fee = $5,000 × 1.5% × 1.5 = $112.50. Total amount due = $5,112.50.

Important Disclaimer

Late fee calculations are estimates based on inputs provided. State usury laws may limit chargeable rates. Always include fee terms in contracts and consult a lawyer for enforcement.

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